Use of Biostimulants as a New Approach for the Improvement of Phytoremediation Performance—A Review

Iodide- and electrochemical assisted removal of mercury by Cirsium arvense from gold tailings in the Amansie West District, Ghana

Mercury (Hg) pollution in Ghana through mining has become a serious environmental challenge. This study investigates the potential of Cirsium arvense to photostabilize Hg using electrokinetic current with or without an iodide solution in gold mine tailings heavily contaminated through mining activities in southern Ghana. An initial Hg concentration of 9.60 mg/kg using cold vapor atomic absorption spectrometry (CVAAS) was determined. The biological absorption coefficient, bioconcentration factor, and translocation factor of Hg have been presented. Cirsium arvense therefore had a higher bioconcentration factor (BCF) of 2.6-5.15 mg/kg, and a transfer factor (TF) of 0.24-0.36 indicating a higher efficiency for phytostabilization. Both the rate and time of extractions of Hg from the tailings by Cirsium arvense are efficiently improved in the combined electric current and iodide treatment. Plant and electric current combined treatment and plant and iodide combined treatment had only 60 and 50% phytostabilization rates, respectively. The combined plant, iodide, and electric current treatment has proven to be superior with about >90% Hg removal rate. Therefore, the combined plant, iodide, and electric current treatment resulted in a higher Hg removal efficiency by Cirsium arvense in a shorter period due to higher solubilization rate and electromigration effects on Hg species.

Phytomanagement of a metal-contaminated agricultural soil with Sorghum bicolor, humic / fulvic acids and arbuscular mycorrhizal fungi near the former Pb/Zn metaleurop Nord smelter

As many contaminated agricultural soils can no longer be used for food crops, lignocellulosic energy crops matter due to their ability to grow on such soils and to produce biomass for biosourced materials and biofuels, thereby reducing the pressure on the limited arable lands. Sorghum bicolor (L.) Moench, can potentially produce a high biomass suitable for producing bioethanol, renewable gasoline, diesel, and sustainable aircraft fuel, despite adverse environmental conditions (e.g. drought, contaminated soils). A 2-year field trial was carried out for the first time in the northern France for assessing sorghum growth on a Cd, Pb and Zn-contaminated agricultural soil amended with humic/fulvic acid, alone and paired with arbuscular mycorrhizal fungi. Sorghum produced on average (in t DW ha-1): 12.4 in year 1 despite experiencing a severe drought season and 15.3 in year 2. Humic/fulvic acids (Lonite 80SP®) and arbuscular mycorrhizal fungi did not significantly act as biostimulants regarding the shoot DW yield and metal uptake of sorghum. The annual shoot Cd, Pb and Zn removals averaged 0.14, 0.20 and 1.97 kg ha-1, respectively. Sorghum cultivation and its metal uptake induced a significant decrease in 0.01 M Ca(NO3)2-extractable soil Cd, Pb and Zn concentrations by 95%, 73% and 95%, respectively, in year 2. Soluble and exchangeable soil Cd, Pb and Zn would be progressively depleted in subsequent crops, which should result in lower pollutant linkages and enhanced ecosystem services. This evidenced sorghum as a relevant plant species for phytomanaging the large area (750 ha) with metal-contaminated soil near the former Pb/Zn Metaleurop Nord smelter, amidst ongoing climate change. The potential bioethanol yield of the harvested sorghum biomass was 5589 L ha-1. Thus sorghum would be a promising candidate for bioethanol production, even in this northern French region.

Biostimulant and Arbuscular Mycorrhizae Application on Four Major Biomass Crops as the Base of Phytomanagement Strategies in Metal-Contaminated Soils

Using contaminated land to grow lignocellulosic crops can deliver biomass and, in the long term, improve soil quality. Biostimulants and microorganisms are nowadays an innovative approach to define appropriate phytomanagement strategies to promote plant growth and metal uptake. This study evaluated biostimulants and mycorrhizae application on biomass production and phytoextraction potential of four lignocellulosic crops grown under two metal-contaminated soils. Two greenhouse pot trials were setup to evaluate two annual species (sorghum, hemp) in Italy and two perennial ones (miscanthus, switchgrass) in China, under mycorrhizae (M), root (B2) and foliar (B1) biostimulants treatments, based on humic substances and protein hydrolysates, respectively, applied both alone and in combination (MB1, MB2). MB2 increased the shoot dry weight (DW) yield in hemp (1.9 times more), sorghum (3.6 times more) and miscanthus (tripled) with additional positive effects on sorghum and miscanthus Zn and Cd accumulation, respectively, but no effects on hemp metal accumulation. No treatment promoted switchgrass shoot DW, but M enhanced Cd and Cr shoot concentrations (+84%, 1.6 times more, respectively) and the phytoextraction efficiency. Root biostimulants and mycorrhizae were demonstrated to be more efficient inputs than foliar biostimulants to enhance plant development and productivity in order to design effective phytomanagement strategies in metal-contaminated soil.

Integrated omics approach reveals the molecular pathways activated in tomato by Kocuria rhizophila, a soil plant growth-promoting bacterium

Plant microbial biostimulants application has become a promising and eco-friendly agricultural strategy to improve crop yields, reducing chemical inputs for more sustainable cropping systems. The soil dwelling bacterium Kocuria rhizophila was previously characterized as Plant Growth Promoting Bacteria (PGPB) for its multiple PGP traits, such as indole-3-acetic acid production, phosphate solubilization capability and salt and drought stress tolerance. Here, we evaluated by a multi-omics approach, the PGP activity of K. rhizophila on tomato, revealing the molecular pathways by which it promotes plant growth. Transcriptomic analysis showed several up-regulated genes mainly related to amino acid metabolism, cell wall organization, lipid and secondary metabolism, together with a modulation in the DNA methylation profile, after PGPB inoculation. In agreement, proteins involved in photosynthesis, cell division, and plant growth were highly accumulated by K. rhizophila. Furthermore, "amino acid and peptides", "monosaccharides", and "TCA" classes of metabolites resulted the most affected by PGPB treatment, as well as dopamine, a catecholamine neurotransmitter mediating plant growth through S-adenosylmethionine decarboxylase (SAMDC), a gene enhancing the vegetative growth, up-regulated in tomato by K. rhizophila treatment. Interestingly, eight gene modules well correlated with differentially accumulated proteins (DAPs) and metabolites (DAMs), among which two modules showed the highest correlation with nine proteins, including a nucleoside diphosphate kinase, and cytosolic ascorbate peroxidase, as well as with several amino acids and metabolites involved in TCA cycle. Overall, our findings highlighted that sugars and amino acids, energy regulators, involved in tomato plant growth, were strongly modulated by the K. rhizophila-plant interaction.

Nitro-PAHs: Occurrences, ecological consequences, and remediation strategies for environmental restoration

Nitrated polycyclic aromatic hydrocarbons (nitro-PAHs) are persistent pollutants that have been introduced into the environment as a result of human activities. They are produced when PAHs undergo oxidation and are highly resistant to degradation, resulting in prolonged exposure and significant health risks for wildlife and humans. Nitro-PAHs' potential to induce cancer and mutations has raised concerns about their harmful effects. Furthermore, their ability to accumulate in the food chain seriously threatens the ecosystem and human health. Moreover, nitro-PAHs can disrupt the normal functioning of the endocrine system, leading to reproductive and developmental problems in humans and other organisms. Reducing nitro-PAHs in the environment through source management, physical removal, and chemical treatment is essential to mitigate the associated environmental and human health risks. Recent studies have focused on improving nitro-PAHs' phytoremediation by incorporating microorganisms and biostimulants. Microbes can break down nitro-PAHs into less harmful substances, while biostimulants can enhance plant growth and metabolic activity. By combining these elements, the effectiveness of phytoremediation for nitro-PAHs can be increased. This study aimed to investigate the impact of introducing microbial and biostimulant agents on the phytoremediation process for nitro-PAHs and identify potential solutions for addressing the environmental risks associated with these pollutants.

Emerging paradigms into bioremediation approaches for nuclear contaminant removal: From challenge to solution

The release of radionuclides, including Cesium-137 (137Cs), Strontium-90 (90Sr), Uranium-238 (238U), Plutonium-239 (239Pu), Iodine-131 (131I), etc., from nuclear contamination presents profound threats to both the environment and human health. Traditional remediation methods, reliant on physical and chemical interventions, often prove economically burdensome and logistically unfeasible for large-scale restoration efforts. In response to these challenges, bioremediation has emerged as a remarkably efficient, environmentally sustainable, and cost-effective solution. This innovative approach harnesses the power of microorganisms, plants, and biological agents to transmute radioactive materials into less hazardous forms. For instance, consider the remarkable capability demonstrated by Fontinalis antipyretica, a water moss, which can accumulate uranium at levels as high as 4979 mg/kg, significantly exceeding concentrations found in the surrounding water. This review takes an extensive dive into the world of bioremediation for nuclear contaminant removal, exploring sources of radionuclides, the ingenious resistance mechanisms employed by plants against these harmful elements, and the fascinating dynamics of biological adsorption efficiency. It also addresses limitations and challenges, emphasizing the need for further research and implementation to expedite restoration and mitigate nuclear pollution's adverse effects.

Plant testing with hemp and miscanthus to assess phytomanagement options including biostimulants and mycorrhizae on a metal-contaminated soil to provide biomass for sustainable biofuel production

The need of biofuels from biomass, including sustainable aviation fuel, without using agricultural land dedicated to food crops, is in constant demand. Strategies to intensify biomass production using mycorrhizal fungi, biostimulants and their combinations could be solutions for improving the cultivation of lignocellulosic plants but still lack well-established validation on metal-contaminated soils. This study aimed to assess the yield of Miscanthus x giganteus J.M. Greef & Deuter and Cannabis sativa L. grown on a metal-contaminated agricultural soil (11 mg Cd, 536 mg Pb and 955 mg Zn kg-1) amended with biostimulants and/or arbuscular mycorrhizal fungi, and the shoot Cd, Pb and Zn uptake. A pot trial was carried out with soil collected from a field near a former Pb/Zn smelter in France and six treatments: control (C), protein hydrolysate (a mixture of peptides and amino acids, PH), humic/fulvic acids (HFA), arbuscular mycorrhizae fungi (AMF), PH combined with AMF (PHxAMF), and HFA combined with AMF (HFAxAMF). Metal concentrations in the soil pore water (SPW), pH and electrical conductivity were measured over time. Miscanthus and hemp shoots were harvested on day 90. Both PH and PHxAMF treatments increased SPW Cd, Pb, and Zn concentrations (e.g. by 26, 1.9, and 22.9 times for miscanthus and 9.7, 4.7, and 19.3 times for hemp in the PH and PHxAMF treatments as compared to the control one, respectively). This led to phytotoxicity and reduced shoot yield for miscanthus. Conversely, HFA and HFAxAMF treatments decreased SPW Cd and Zn concentrations, increasing shoot yields for hemp and miscanthus. Shoot Cd, Pb, and Zn uptakes peaked for PH and PHxAMF hemp plants (in μg plant-1, Cd: 310-334, Pb: 34-38, and Zn: 232-309 for PHxAMF and PH, respectively), while lowest values occurred for PH miscanthus plants mainly due to low shoot yield. Overall, this study suggested that humic/fulvic acids can be an effective biostimulant for increasing shoot biomass production in a metal-contaminated soil. These results warrant further investigations of the HFAxAMF in field trials.

Phytoremediation of Pollutants: Applicability and Future Perspective

Environmental pollution is a global issue since it is spreading worldwide, affecting entire ecosystems [...].

Bacterial Communities Associated with the Roots of Typha spp. and Its Relationship in Phytoremediation Processes

Heavy metal pollution is a severe concern worldwide, owing to its harmful effects on ecosystems. Phytoremediation has been applied to remove heavy metals from water, soils, and sediments by using plants and associated microorganisms to restore contaminated sites. The Typha genus is one of the most important genera used in phytoremediation strategies because of its rapid growth rate, high biomass production, and the accumulation of heavy metals in its roots. Plant growth-promoting rhizobacteria have attracted much attention because they exert biochemical activities that improve plant growth, tolerance, and the accumulation of heavy metals in plant tissues. Because of their beneficial effects on plants, some studies have identified bacterial communities associated with the roots of Typha species growing in the presence of heavy metals. This review describes in detail the phytoremediation process and highlights the application of Typha species. Then, it describes bacterial communities associated with roots of Typha growing in natural ecosystems and wetlands contaminated with heavy metals. Data indicated that bacteria from the phylum Proteobacteria are the primary colonizers of the rhizosphere and root-endosphere of Typha species growing in contaminated and non-contaminated environments. Proteobacteria include bacteria that can grow in different environments due to their ability to use various carbon sources. Some bacterial species exert biochemical activities that contribute to plant growth and tolerance to heavy metals and enhance phytoremediation.

Immobilization effects of co-pyrolyzed neem seed mixed with poultry manure on potentially toxic elements in soil and the phytoremediation potentials of native Manihot esculenta and Jatropha curcas in ensuring sustainable land use

This study evaluated the effects of neem seed biochar, poultry manure, and their combinations at varying rates of 15 and 25% (w/w) on potentially toxic elements (PTEs) in soils. Afterward, the suitability of Manihot esculenta and Jatropha curcas in removing Cd, As, Zn, Pb, and Hg from mine spoils were appraised in a 270-day outdoor pot experiment. Using ICP-Mass Spectrometry, the elemental contents of target PTE in the shoot, root, and soil specimens were determined for each treatment. The obtained average values were further subjected to a nonparametric test of samples using IBM SPSS Statistic 29. The applied organic amendments resulted in significant differences p < 0.05 in PTE availability for plant uptake after the Independent-Samples Kruskal-Wallis Test was made. Nonetheless, applying a 25% (w/w) mixture of neem seed biochar and poultry manure was efficient in immobilizing more PTEs in soils which caused lower PTEs presence in plants. Organic amendments further significantly enhanced the fertility of the mine soils leading to about a 6- 25.00% increase in the biomass yield (p < 0.05) of both plants. No significant difference (p > 0.05) was however observed between the phytoremediation potentials of both plants after the Independent-Sample Mann-Whitney U test. Even that, Manihot esculenta was averagely more efficient in PTE uptake than Jatropha curcas. Larger portions of the bioaccumulated PTEs were stored in the roots of both plants leading to high bioconcentration factors of 1.94- 2.47 mg/kg and 1.27- 4.70 mg/kg, respectively, for Jatropha curcas and Manihot esculenta. A transfer factor < 1 was achieved for all PTEs uptake by both plants and indicated their suitability for phytostabilization. Techniques for easy cultivation of root-storing PTEs are required to enhance their large-scale use as their biomass could further be used in clean energy production.

Arbuscular Mycorrhizal Fungi and Compost-Based Biostimulants Enhance Fitness, Physiological Responses, Yield, and Quality Traits of Drought-Stressed Tomato Plants

Climate change-driven water resource constraints cause tomatoes to suffer from drought. The use of biostimulants has emerged as an important approach to enhancing resilience to drought. However, the roles of biostimulants in the physicochemical characteristics of tomatoes in response to drought are poorly understood. In this study, we evaluated the ability of arbuscular mycorrhizal fungi (AMF) and compost (versus NPK application) to improve the agro-physiology, yield, and fruit quality of tomato plants and their tolerance to drought by comparing them with conventional chemical fertilizers (NPK). Under drought conditions, plant growth traits associated with yield and fruit bioactive compounds (carotenoids: 73%; lycopene: 53%; polyphenols: 310%; and flavonoids: 158%) were increased in the AMF-tomato treatment. Compost significantly enhanced sugars (ca. 60%) and protein contents (ca. 20%). Moreover, AMF protected the photosynthetic apparatus from drought-induced oxidative stress, improved photosynthetic efficiency, leaf water potential, and osmolytes, and reduced malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) accumulation by increasing peroxidase (POX) (140%) and polyphenol oxidase (PPO) (340%) activities compared to their controls. Our findings revealed that NPK is an important nutrient-based fertilizer for plant growth and development. However, its efficiency as a fertilizer is quite low. In addition, we highlighted different mechanisms mediated by AMF and compost, inducing drought tolerance in tomato plants.

Study of Applying Naturally Occurring Mineral Materials for Silicone Pressure-Sensitive Adhesives

Silicones are commonly used as adhesives when high-quality materials are required due to harsh environmental conditions such as high temperature, humidity, etc. To ensure high resistance to environmental conditions, including high temperatures, modifications of silicone adhesives are made using fillers. The characteristics of a modified silicone-based pressure-sensitive adhesive with filler are the focus of this work. Functionalized palygorskite was prepared in this investigation by grafting 3-mercaptopropyltrimethoxysilane (MPTMS) onto palygorskite (palygorskite-MPTMS). The palygorskite was functionalized using MPTMS under dried conditions. FTIR/ATR spectroscopy, thermogravimetric analysis, and elemental analysis were all used to characterize the obtained palygorskite-MPTMS. MPTMS loading onto palygorskite was also proposed. The results demonstrated that palygorskite's initial calcination favors the grafting of functional groups on its surface. New self-adhesive tapes based on palygorskite-modified silicone resins have been obtained. This functionalized filler allows for the improvement of the compatibility of palygorskite with specific resins for application in heat-resistant silicone pressure-sensitive adhesives. The new self-adhesive materials showed increased thermal resistance while maintaining good self-adhesive properties.

The Response of Purslane (Portulaca oleracea) to Soil-Added Pb: Is It Suitable as a Potential Phytoremediation Species?

Soils with high lead (Pb) levels can be decontaminated with the use of tolerant plants. Their effectiveness may be increased with added soil N due to boosted plant vigor, but such an agronomic practice has not been widely reported so far. In this work, purslane (Portulaca oleracea) was tested in a pot experiment as a potential phytoremediation species using soil spiked with Pb at doses of 0, 150, 300, 600, and 900 mg kg^-1 (referred to as Pb(0), Pb(150), Pb(300), Pb(600), and Pb(900), respectively) with added N (referred to as N(1); at 300 kg N ha^-1) and without added N (N(0)). We found that added Pb did not cause any adverse effects on plant growth (height, and aerial and root dry biomass) and physiological parameters, which were boosted with added N. Lead plant concentration and uptake significantly increased with added N, a finding that confirms our hypothesis. The number of necessary harvests of purslane in order to reduce soil Pb to half its initial concentration was also calculated and found to decrease with added N, being 131 at Pb(900)N(1). Although results indicate the potential of purslane as a phytoremediation species, further research is needed under real field conditions.

Phytoremediation of Potentially Toxic Elements: Role, Status and Concerns

Environmental contamination with a myriad of potentially toxic elements (PTEs) is triggered by various natural and anthropogenic activities. However, the industrial revolution has increased the intensity of these hazardous elements and their concentration in the environment, which, in turn, could provoke potential ecological risks. Additionally, most PTEs pose a considerable nuisance to human beings and affect soil, aquatic organisms, and even nematodes and microbes. This comprehensive review aims to: (i) introduce potentially toxic elements; (ii) overview the major sources of PTEs in the major environmental compartments; (iii) briefly highlight the major impacts of PTEs on humans, plants, aquatic life, and the health of soil; (iv) appraise the major methods for tackling PTE-caused pollution; (v) discuss the concept and applications of the major eco-technological/green approaches (comprising phytoextraction, rhizofiltration, phytostabilization, phytovolatilization, and phytorestoration); (vi) highlight the role of microbes in phytoremediation under PTE stress; and (vii) enlighten the major role of genetic engineering in advancing the phytoremediation of varied PTEs. Overall, appropriate strategies must be developed in order to stop gene flow into wild species, and biosafety issues must be properly addressed. Additionally, consistent efforts should be undertaken to tackle the major issues (e.g., risk estimation, understanding, acceptance and feasibility) in order to guarantee the successful implementation of phytoremediation programs, raise awareness of this green technology among laymen, and to strengthen networking among scientists, stakeholders, industrialists, governments and non-government organizations.

Changes in the Phytochemical Profile and Antioxidant Properties of Prunus persica Fruits after the Application of a Commercial Biostimulant Based on Seaweed and Yeast Extract

Plant biostimulants are formulations that are experiencing great success from the perspective of sustainable agriculture. In this work, we evaluated the effect derived from the application of a biostimulant based on algae and yeast extracts (Expando^®) on the agronomic yield and nutraceutical profile of two different cultivars ("Sugar Time" and "West Rose") of Prunus persica (peach). Although, at the agronomic level, significant effects on production yields were not recorded, the biostimulant was able to reduce the ripening time, increase the fruit size, and make the number of harvestable fruits homogeneous. From a nutraceutical point of view, our determinations via spectrophotometric (UV/Vis) and chromatographic (HPLC-DAD-MS/MS) analysis showed that the biostimulant was able to boost the content of bioactive compounds in both the pulp (5.0 L/ha: +17%; 4.0 L/ha: +12%; 2.5 L/ha: +11%) and skin (4.0 L/ha: +38%; 2.5 L/ha: +15%). These changes seem to follow a dose-dependent effect, also producing attractive effects on the antioxidant properties of the fruits harvested from the treated trees. In conclusion, the biostimulant investigated in this work proved to be able to produce more marketable fruit in a shorter time, both from a pomological and a functional point of view.